Boost carousel arrows only allow a single step in multicolumn mode

**Describe the bug**

When using multicolumn layout, the boost carousel only lets you scroll by a single boost. Further clicking of the right arrow does nothing. This does not happen in the "floating" layout.

- This happens on both dev.phanpy.social and phanpy.social
- instance: toot.cat

**To Reproduce**
Steps to reproduce the behavior:
1. Set up a 4-column multicolumn layout on desktop, including a Following column
2. Scroll around until you find a boost carousel
3. Click on the right arrow to see the second boost (this works fine)
4. Click on the right arrow again to see the third boost (this does not work)

**Expected behavior**
I should be able to scroll through all boosts in the carousel

**Screenshots**

**Desktop (please complete the following information):**
- OS: Windows
- Browser Firefox
- Version 118.0.2

Start by reproducing the carousel in a four-column multicolumn layout with a Following column, then compare its arrow behavior with the floating layout. The fix is complete when repeated right-arrow clicks can show every boost in the carousel, including the third and later boosts.

Written by the indexing model from the issue text.